Effects Of Soy Peptides On Immune And Digestive Function Of Piglets

Soy peptides were minor peptides in which the soybean protein was hydrolyzed by compound protease. Their low molecular weight of mainly 180-500 Da made them have higher application value. The effects of soy peptides on blood chemical indexes, intestinal morphology and digestive enzyme activities, redox state as well as immune function and expression level of cytokine related genes and innate immune receptor genes in piglets were studied in this paper. The function and possible mechanism of soy peptides was explored preliminarily, thus to provide certain theoretical basis for the development of soy peptides as a novel and secure protein ingredients.Firstly, antioxidant activities of soy peptides in vitro were determined by the indexes of the clearance rate of DPPH· and ·OH. Then twelve ear-tagged 7-d old piglets(Duroc× Landrace× Large Yorkshire) were randomly divided into two groups, each consisting of three male and three female piglets. A 14-d treatment period then followed on every nine o’clock am, during which intra-gastric infusions of 250 mg/kg· bw-1 soy peptides and 254 mg/kg· bw-1 L-alanine were conducted respectively to the experimental and control piglets. All piglets were nursing conventionally by sows and fed with formula feeds of suckling piglets at the same time during the whole experiment. Initial and final weight were recorded and samples were collected after slaughtering at the end of the trial. Based on the former experiment, 144 ear-tagged 25-d weaned piglets(Duroc× Landrace× Large Yorkshire) were randomly assigned to four treatments, with three replicates in every treatment and twelve piglets in every replicate. The four treatments were fed with diets respectively containing different doses of soy peptides(0, 5, 10 and 20 g/kg). Feeding period lasted for 28 days. Initial and final weight as well as feed consumption of piglets were recorded. Twelve piglets were randomly selected from every treatment for blood sampling through precaval vein at the end of the experiment. Results showed that:(1) the clearance rate of soy peptides on DPPH· and ·OH was as high as 98.33%, 84.38% respectively, suggesting that soy peptides played a good role in scavenging free radicals with higher antioxidant capacity.(2) compared with the control group, soy peptides improved daily weight gain and blood glucose concentration of the piglets, and significantly reduced the content of plasma urea nitrogen(P<0.05); crypt depth was significantly decreased, the ratio of villus height and crypt depth(P<0.05) as well as the activities of trypsin(P<0.05) and disaccharide enzyme(P<0.01) were notably enhanced in duodenum, jejunum and ileum; the relative amounts of Peyer’s patches(PP) in ileum were significantly increased; the contents of plasma Ig G, IL-6 and IFN-γ as well as concentrations of s Ig A, IL-6 and IFN-γ in ileum mucosa were also elevated significantly(P<0.01); the activities of SOD were enhanced remarkably(P<0.01) in plasma and tissue(liver, spleen, duodenum, jejunum, ileum), and the capacity of T-AOC in plasma was also notably reinforced(P<0.01); the correlation analysis showed that plasma T-AOC and SOD activities were significantly positively related to the content of Ig G; significantly up-regulatory effects(P<0.05) were appeared in the gene expression of IFN-γ, IL-6, IL-10, FOXP3 and TGFβ1 in ileum mucosa and liver as well as TLR2, TLR4, TLR9 and NF-kappa B2 in ileum(P <0.05).(3) soy peptides with the dose of 10 g/kg could significantly improve daily weight gain and daily feed intake of weaned piglets(P<0.05), and remarkably decrease the ratio of feed to weight gain(P<0.05); at the same time notab ly enhanced effects were also observed in the content of plasma Ig G、Ig M、IL-6 and IFN-γ(P<0.05) in weaned piglets.In conclusion, soy peptides could promote the development of intestinal mucosa structure and improve the activities of digestive enzymes, thus promoting digestion and absorption and effectively enhancing growth performance of piglets. Besides soy peptides were conducive to improving antioxidant capacities and increasing expression level of immune-related genes, thus increasing contents of Ig G and s Ig A and enhancing the immune function of piglets for better health.